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OCULAR ACCOMMODATION
Studies of amplitude, insufficiency, and
facility training in young school children
Bertil Sterner
Department of Ophthalmology
Institute of Clinical Neuroscience
Göteborg University
2004
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ISBN 91-628-5989-7
© Bertil Sterner
Department of Ophthalmology
Institute of Clinical Neuroscience
Göteborg University
Sweden
Printed by Vasastadens Bokbinderi AB
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ABSTRACT
The purpose of this thesis was to establish the sufficiency of the ocular
accommodation and to characterize accommodative problems and related
symptoms among otherwise healthy young school children. The purpose
was also to evaluate an accommodative facility training technique by
studying the effect of the training on relative accommodation.
Children from a junior level school were invited to participate in an
examination of the accommodative function which was then compared to
expected age levels. Children aged 9–13 years, referred by School Health
Care for near work-related problems and complaining of headaches,
blurred vision, asthenopia, loss of concentration, and avoidance of near
activity, were also studied. Only children with reduced negative relative
accommodation (NRA) and positive relative accommodation (PRA) and/or
very slow accommodative facility were included. The subjects used an
accommodative facility training technique until they reported that the
symptoms had disappeared.
The results showed lower amplitudes than expected in a large group of
children and not equivalent to the expected age values. More than one third
of the children reported subjective symptoms at near. The incidence of
subjective symptoms emerged at the age of 7.5 years and there was
significant discrimination ability between low amplitude and subjective
symptoms.
In all of the trained children the symptoms gradually decreased and finally
disappeared during the training period. The data showed a significant
increase, despite some individual variations, in both mean NRA and mean
PRA among all children characterized with accommodative infacility due
to an impaired relative accommodation.
Accommodation is not as sufficient in young children as expected.
Subjective symptoms emerge at the age of 7.5 years and there is a clear
relation between accommodative parameters and these subjective
symptoms. Clear standards for diagnosing an accommodative dysfunction
need to be further refined. The results also indicate that accommodative
facility training is an effective method resulting in loss of symptoms and
that it also has a real effect on the relative accommodation in patients with
impaired relative accommodation. Because accommodative dysfunctions
may result in subjective symptoms, it is of great importance to identify this
dysfunction to prevent unnecessary near vision problems.
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APPENDED PAPERS
This work is based on following papers:
Paper I.
Sterner B., Gellerstedt M., Sjöström A. The amplitude of accommodation
in 6–10-year-old children – not as good as expected! (Accepted for
publication, Ophthalmic and Physiological Optics).
Paper II.
Sterner B., Gellerstedt M., Sjöström A. Accommodative insufficiency,
subjective symptoms, and reference values for young school children.
(Submitted).
Paper III.
Sterner B., Abrahamsson M., Sjöström A. (1999). Accommodative facility
training with a long term follow up in a sample of school aged children
showing accommodativedysfunction. Documenta Ophthalmologica 99:
93–101.
Paper IV.
Sterner B., Abrahamsson M., Sjöström A. (2001). The effects of
accommodative facility training on a group of children with impaired
relative accommodation - a comparison between dioptric treatment and
sham treatment. Ophthalmic and Physiological Optics. 21: 470-476.
The papers are reproduced with kind permission from Kluwer Academic
Publishers and Blackwell Publishing.
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ABBREVIATIONS
AC/A
C
CA
CNS
cpm
D
DA
NRA
NRM
PC
PRA
PRM
SD
TA
Accommodative convergence/accommodation
Convergence
Convergence accommodation
Central nervous system
Cycles per minute
Diopter
Prismatic diopter
Dark accommodation
Negative relative accommodation
Negative relative movement
Point of convergence
Positive relative accommodation
Positive relative movement
Standard deviation
Tonic accommodation
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TABLE OF CONTENTS
INTRODUCTION .................................................................................... 1
The mechanism of accommodation.................................................. 1
Neural pathways ............................................................................... 3
Accommodative measurements........................................................ 6
Stimuli to accommodation ........................................................ 6
Amplitude of accommodation................................................... 6
Facets of accommodation ......................................................... 8
Accommodative measurements............................................... 13
Accommodative dysfunction .......................................................... 14
Presbyopia .............................................................................. 14
Dysfunction ............................................................................ 15
Asthenopia.............................................................................. 16
Accommodative therapy................................................................. 19
OBJECTIVES ........................................................................................ 21
SUBJECTS ............................................................................................. 23
METHODS ............................................................................................. 25
RESULTS ............................................................................................... 27
DISCUSSION ......................................................................................... 31
CONCLUSIONS..................................................................................... 37
FUTURE STUDIES................................................................................ 38
ACKNOWLEDGMENTS ...................................................................... 39
REFERENCES ....................................................................................... 41
APPENDED PAPERS (I - IV)
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B. STERNER. OCULAR ACCOMMODATION.
1
INTRODUCTION
The mechanism of accommodation
Accommodation is the ability of the eye to change the refractive power of
the lens and automatically focus objects at various distances on the retina.
The accommodative process, which involves the accommodative apparatus
illustrated in Figure 1, includes contraction of the ciliary muscle, which
releases the tension on the zonular fibers, allowing the elastic lens capsule
to increase its curvature, especially that of the front surface. Along with
these changes, an increase in the thickness of the lens, a decrease in its
equatorial diameter, and a reduction in pupil size take place (Brown, 1972)
(Figure 2).
Figure 1. The accommodative apparatus.
Accommodation is measured in diopters (D), which is the reciprocal of the
fixation distance. Thus, if the fixation distance is 1 m, the accommodation
is said to be 1 D; if it is 0.5 m or 0.33 m, the accommodation is 2 D or 3 D,
respectively.
The furthest distance at which an object can be seen clearly is called the far
point (punctum remotum). In order to see such an object the eye is in a
state of rest, the ciliary muscle is relaxed, and the refractivity is at
minimum.
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B. STERNER. OCULAR ACCOMMODATION.
Figure 2. Schematic picture of the lens and the ciliary muscle when relaxed
during ”distance” vs accommodated during ”near” vision.
When maximum accommodation is in force, the nearest point which the
eye can see clearly is called the near point (punctum proximum). The
difference between the refractivity of the eye in the two conditions – when
at rest with minimal refraction, and when fully accommodated with
maximal refraction – is called the amplitude of accommodation. In order to
accurately perform visually guided daily tasks, it is necessary for the
accommodative system to be dynamic, fast, and precise to ensure a wellfocused image on the retina.
It has been known for over 50 years that, under certain conditions,
accommodative activity in the eyes may act as a stimulus which produces a
change in the relative position of the visual axes as a response (Morgan,
1944a). When the angle formed by the visual axes increases this is called
convergence, and when it decreases, we call this divergence. In addition,
with fixation at near pupillary constriction, miosis occurs (Jampel, 1959;
Von Noorden, 1985). The synkinetic association between accommodation,
convergence, and miosis during fixation at near may be termed the near
vision complex or near response.
The accommodative act is normally accompanied by a change in
convergence because of the synkinetic association between the ciliary
muscle and the medial recti muscle (of the eye) (Duke-Elder. 1971). An
accommodative stimulus acts as a trigger which excites innervational
mechanisms for convergence. This response of convergence due to the
accommodation constitutes accommodative convergence. However, due to
B. STERNER. OCULAR ACCOMMODATION.
3
the synkinetic association, a stimulus for convergence can also provoke an
accommodative impulse called convergence accommodation.
Neural pathways
The afferent pathways that stimulate accommodation and the light reflex
emanate from retinal receptors. Impulses are propagated through the nervus
opticus, the chiasma, and the tractus opticus to corpus geniculatum
laterale. The pupillomotoric nerves involved in the light reflex, unlike the
visual pathways, project without any synaptic connections in corpus
geniculatum laterale directly to nucleus pretectale and to the EdingerWestphal nucleus (Figure 3). Following nervus oculomotorius, the efferent
signals travel via ganglion ciliare into musculus sphincter pupillæ (Walsh
and Hoyt 1969a).
The afferent sensory visual pathways have a synapse in corpus geniculatum
laterale and proceed to the primary visual cortex.
Figure 3. Neural pathways involved in the light reflex and accommodation.
Pathways and areas in the CNS (central nervous system) that are related to
accommodation and vergence eye movements as described by Gamlin
(2002) are schematically illustrated in Figure 4. Pathways to areas that are
known to be, or based on anatomical studies or electrophysiological studies
believed to be related to accommodation and vergence eye movements are
also illustrated.
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B. STERNER. OCULAR ACCOMMODATION.
Figure 4. Schematic illustration of neural pathways involved in the control of
accommodation and vergence eye movements in CNS. Pathways to areas that are
known to be, or based on anatomical studies or electrophysiological studies believed to
be related to accommodation and vergence eye movements, are shown with solid lines.
The pathways and areas that remain to be identified are shown with dotted lines and
question marks.
The efferent pathways, both parasympathetic and sympathetic fibres,
involved in the accommodative process as described by Richter et al.
(2000) are illustrated in Figure 5.
B. STERNER. OCULAR ACCOMMODATION.
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Figure 5. Illustration of the efferent pathways, both parasympathetic and sympathetic
fibres, involved in the accommodative process. The major innervation to the ciliary
muscle is parasympathetic and originate in the Edinger-Westphal nucleus. The fibres
follow Nervus oculomotorius and synapse in the ciliary ganglion. Most of the
postganglionic parasympathetic fibres travel to the ciliary muscle via the short ciliary
nerves, but some of them (14) also travel with the long ciliary nerves. A direct pathway
of uncertain functional significance (11) to the internal eye structures from the EdingerWestphal nucleus is also illustrated. The sympathetic innervation of the ciliary muscle
starts in the diencephalon and travels caudally down to the lower cervical and upper
thoracic segments to synapse in the ciliospinal centre of the spinal cord. From there,
second-order neurones leave the cord by the last cervical and first thoracic ventral roots;
these preganglionic fibres run up the cervical chain to synapse in the cervical ganglion.
The third-order neurones continue up the sympathetic carotid plexus and enter the eye,
either with the trigeminal nerves first division (following the nasociliary division) or
independently, where they join the long and short ciliary nerves, in the latter instance
passing through the ciliary ganglion without synapse (Richter et al., 2000).
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B. STERNER. OCULAR ACCOMMODATION.
Accommodative measurements
Stimuli to accommodation
The characteristics of effective accommodative stimuli are central to our
understanding of the accommodative system. There are a number of
different accommodative stimuli which stimulate accommodation to a
varying degrees (Sivak & Bobier, 1978; Kruger & Pola, 1985; McLin Jr et
al., 1988; Comerford & Thorn, 1990; Siderov & Johnston, 1990;
Rosenfield et al., 1991; Gray et al., 1993; Mathews & Kruger, 1994;
Rosenfield & Cohen, 1995; Kruger, Aggarwala et al. 1997; Kruger,
Mathews et al., 1997):
•
•
•
•
•
•
Blur of the object
Proximity of the target
Changing target size
Chromatic abberation
Convergence of the eyes
Spatial frequency
These are all different stimuli to accommodation, with blur of the object
having the greatest impact as an accommodative stimulus, though
dependent on visual acuity (White & Wick, 1995). However, an important
implication is the completely different character of these accommodative
stimuli, which can act together as well as individually. The inherent
differences between the stimuli therefore require that different methods be
used to describe them.
Amplitude of accommodation
The ability to accurately focus a visual target at varying distances exists to
some extent from birth (Banks, 1980a), but improves rapidly in the first
3–6 months of life (Banks, 1980b; Howland, 1982–83; Hainline et al.,
1992; Bobier et al., 2000). It is belived that a small child is normally able
to focus from infinity down to a distance close to the eyes because of a high
level of accommodative amplitude. However, accommodation and
convergence are not evidently automatically linked from the start
(Hainlineet al., 1992).
In 1912, Duane presented his result on the accommodative amplitude
among 1000 subjects aged 8 to 70 years. The given data are still commonly
used as normality for accommodative amplitude in relation to age. A
B. STERNER. OCULAR ACCOMMODATION.
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formula based on Duane’s data, (minimum amplitude = 15 – 0.25 · age,
expected amplitude = 18.5 – 0.3 · age, and maximum
amplitude=25–0.4·age), predicts the range of accommodative amplitude
expected at a given age (Hofstetter, 1950) (Figure 6). Because there were
only 35 eyes between 8 to 12 years of age the reliability of this “normality”
for these ages has been discussed (Turner, 1958; Wold, 1967; Kragha,
1986). Based on this formula, a 3 year old child is expected to have an
average accommodative amplitude of 17.6 D. A study by McBrien and
Millodot(1986) shows different data on accommodative amplitude linked
to ametropia among 18-22-year-old subjects (i.e., late-onset myopes:
mean10.77D; earlier-onset myopes: mean 9.87 D; emmetropes: mean
9.28D; and hyperopes: mean 8.63 D). This is an issue to consider in
discussing the normality of the accommodative amplitude.
Figure 6. The classic diagram from Duane (1912) showing the relation between
age (x-axis) and accommodative amplitude in diopters (y-axis), with each dot
representing the maximum amplitude of accommodation in an individual eye at a
given age. The straight line is a plot of the prediction formula (expected
amplitude= 18.5 – 0.3 · age) by Hofstetter (1950).
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B. STERNER. OCULAR ACCOMMODATION.
Facets of accommodation
The accommodative function is normally explained, although
insufficiently, by describing the accommodative amplitude and its dioptric
value. However, the accommodative function is more complicated than
that. The accommodative system is complex; the different facets of the
accommodative function, beside the amplitude, are described and explained
elsewhere in the literature (Rouse et al., 1984; Wick & Hall, 1987;
Michaels, 1987; Rosner & Rosner, 1989; Von Noorden & Avilla, 1990;
Ebenholtz, 1991; Miwa & Tokoro, 1993).
Different facets of the accommodative function, together with
accommodative amplitude, are listed below:
•
•
•
•
•
Tonic accommodation
Lag of accommodation
Convergence accommodation
Accommodative facility
Relative accommodation
These facets differ greatly from each other with regard to function. They
require different methods of examination and they are not explained by the
same dioptric values; nor is a unified system of measurement used for their
dioptric results.
Each of the accommodative facets listed above is described below.
However, in this thesis, I will concentrate on the amplitude of
accommodation, accommodative facility, and relative accommodation with
regard to function, method of examination, and expected dioptric value. In
the case of failure of function, associated symptoms will be described.
Tonic accommodation
Tonic accommodation (TA), or dark accommodation (DA)
(Tsuetaki&Schor, 1987; Rosner & Rosner, 1989; Ebenholtz, 1991;
Rosenfield et al., 1992; Chiu & Rosenfield, 1994; Rosenfield et.al., 1994),
is the passive state of accommodation in the absence of a stimulus, that is,
when the eye is either in complete darkness, or when it is looking at a
bright empty field (open-loop). One method of measuring the open-loop is
by using an objective infrared optometer (Gray et al., 1998).
B. STERNER. OCULAR ACCOMMODATION.
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Lag of accommodation
The amount by which the accommodative response of the eye is less than
the dioptric stimulus to accommodation is defined as accommodative lag
(Rouse et al., 1984; Wick & Hall, 1987; Goss & Zhai, 1994). Clinical
measurement of accommodative lag at near is typically done using
dynamic retinoscopy. This is an objective method in which the patient
views a near point target, while the examiner adjusts the lens power, uses a
“skia ladder”, or his or her distance from the patient.
Convergence accommodation
Convergence accommodation is normally described by the ratio between
convergence accommodation and convergence, or the CA/C ratio (Morgan,
1944a). The ratio is a measure of the effect of a change in convergence on
accommodation. It is expressed as the change in accommodation (in D) for
each change in convergence (in prism D) (Tsuetaki & Schor, 1987).
Accommodative facility
Accommodative facility is the ability to rapidly change the refractive
power of the lens to various focus distances (Wick & Hall, 1987) while
maintaining a requisite angle of convergence (binocular) or eliminating the
influence of convergence (monocular). This ability is important when
changing fixation from near to distance, and back again.
Clinically, accommodative facility can be measured using lenses that
stimulate (minus) or inhibit (plus) accommodation. Any combination of
lens power can be used for evaluation, but empirical testing has indicated
that ±2.00 D is a reasonable choice (McKenzie et al., 1987). The testing
procedure uses ±2.00 D lens pairs mounted in a flipper frame. A “flipper”
is a holder with two minus lenses and two plus lenses (Figure 7).
Figure 7. Flip lenses.
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B. STERNER. OCULAR ACCOMMODATION.
The subject focuses through one pair of lenses at an object at near distance
(40 cm). When the object is clearly focused, a flip is quickly performed to
the other lens pair and the subject focuses through them. This is then
repeated and the number of cycles completed in 1 minute (cpm) is recorded
as the accommodative facility.
Normative data on monocular as well as binocular accommodative facility
have been collected on both adult pre-presbyopic populations
(Zellersetal., 1984; Siderov & Diguglielmo, 1991) and young school
children (Hennessey et al., 1984; Scheiman et al., 1988;
Jackson&Goss,1991a) (Table 1). In the study by
Siderov&Diguglielmo(1991), adults between 30 years and 42 years of
age showed a mean and SD for the ±2.00 flip task of 1.2 ±2.1 cpm
binocularly. Another study, by Zellers et al. (1984), of adults aged
18–30years, had a mean and SD for the binocular ±2.00 flip task of
7.72±5.15 cpm. Two studies of young school children aged 6–12 reported
means and SDs on the binocular ±2.00 flip task. Results were 5.0 ±2.7 cpm
in one study (Jackson & Goss, 1991a), and 3.83 ±2.5 cpm in another
(Scheiman et al., 1988). One reason for the lower mean cpm in this age
group, as compared with the results for 18–30-year-olds, may be the
difference in instructional sets. Instead of the subjects holding the flip lens,
as with the adult groups, the examiner held it. One also has to consider
possible differences with respect to the age and the time necessary for
saying “clear” (Kedzia et al. 1999).
Table 1. Binocular accommodative facility in cpm (mean ± SD) using ±2.00 D flip
lenses.
Age 6-12 years
Jackson & Goss
Scheiman et al.
Zellers et al.
Siderov & Diguglielmo
Age 18-30 years
Age 30-42
years
5.0 ± 2.7
3.83 ± 2.5
7.72 ± 5.15
1.2 ± 2.1
The monocular (Rouse et al., 1989) and binocular (Rouse et al., 1992)
accommodative facility rates have previously been studied in an attempt to
establish normative data and cutoff values which differentiate symptomatic
from asymptomatic subjects (McKenzie et al., 1987; Garcia et al., 2000).
The 1-minute testing method appears reliable if the initial rate is lower than
3 cpm. For patients whose initial rate is between 3 cpm and 8cpm,
extended testing (i.e., 1–2 minutes’ additional testing) may be needed to
arrive at an accurate diagnosis.
B. STERNER. OCULAR ACCOMMODATION.
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Relative accommodation
The total amount of accommodation, which can be exerted while the
convergence of the eyes is fixed, is called relative accommodation
(Morgan, 1944a). This can be either positive relative accommodation
(PRA) or negative relative accommodation (NRA). The PRA is the amount
of accommodation in excess of the accommodation needed for convergence
and the NRA is the amount of accommodation below that of convergence
(Gettes, 1957) (Figure 8).
Figure 8. The relation between positive relative accommodation (PRA), negative
relative accommodation (NRA), and the point of convergence (PC). The dotted
lines in the Figure describe the point the accommodation is focused to when a plus
lens (for NRA) or a minus lens (for PRA) is added without changing the
convergence stimuli. The positive relative movement (PRM) and negative relative
movement (NRM) describe the direction of the different dioptric focus change
movements of the PRA and the NRA in relation to the PC.
Hung & Ciuffreda (1994) describe how relative accommodation is
measured. In assessing accommodative flexibility, with a constant
convergence stimulus and under binocular fusion, the accommodative
stimulus was binocularly decreased. This is done by starting with positive
lenses and continuing in +0.25 D steps over the distance correction, with
the vergence stimulus (at 40 cm) held constant, until the first slight
sustained blur is subjectively noted by the patient. The decreased amount of
accommodative stimulus at this point is referred to as the NRA value. Back
to distance correction, and if the accommodative stimulus is now increased
binocularly with negative lenses in –0.25 D steps until the first slight
sustained blur is again noticed, the increased amount of accommodative
stimulus at this point is referred to as PRA.
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B. STERNER. OCULAR ACCOMMODATION.
Means for NRA and PRA in 800 subjects all of whom had an
accommodative amplitude of 5.00 D or more, have been presented in
Goss& Zhai (1994), to be +2.00 ±0.50 D and –2.37 ±1.12 D, respectively.
In the same study, 1000 school children from first to twelfth grade had a
mean NRA of +1.75 ±0.56 D and a mean PRA of –2.37 ±1.00 D.
An important question at this point is what happens with the NRA/PRA
value if we add prismatic diopter ()? Is it possible, for example, to
increase the NRA value if we add base in prism? We know by hearsay that
6 with prismatic base in will increase the NRA value by approximately
+0.50 D, but could not find any evidence in the literature for this relation.
Due to the near vision complex, a certain portion of convergence is linked
when accommodation is in force. The relation between the dioptric change
of the accommodation and the prismatic change of the convergence is
called the accommodative convergence/accommodation (AC/A) ratio. The
AC/A ratio describes how much accommodative convergence is activated
by an accommodative change of 1 D. In Table 2, the relationship between
high, normal, and low AC/A ratios and the different convergence stimuli is
described.
Table 2. The relation between the AC/A ratio and the convergence stimuli when
accommodation is changed by ± 2.00 D.
AC/A
“High”
“Normal”
“Low”
AC/A ratio
(/D)
>5
3 to 5
<3
Convergence stimuli
()
>±10.0
±6.0 to ±10.0
<±6.0
The normal range of the AC/A ratio is between three and five. Values above five are
considered to denote excessive accommodative convergence and values below three an
insufficiency (von Noorden & Avilla, 1990).
In individuals with high AC/A ratio the larger convergence stimuli induced
by the changed accommodation may affect the measured threshold of the
PRA and/or the NRA if the fusional vergence is at its limit.
If a prismatic lens is added in front of the eye, thereby changing the
convergence stimuli, a change in accommodation will be expected. If we
add a base in prism in front of the eye the convergence stimuli will change
to a point further away from the eye. As a result, the PRA value will
decrease and the NRA value will increase.
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B. STERNER. OCULAR ACCOMMODATION.
The correlation of PRA with prismatic base in blur at near distance is to be
expected because the amount of PRA a person can exert may be limited by
his or her negative fusional vergence capability (i.e., divergence with
fusion at the same stimuli). There is a similar correlation between NRA
with near base-out blur because NRA may be limited by the amount of
available positive fusional vergence (i.e., convergence with fusion at the
same stimuli) (Jackson & Goss, 1991b).
Tests for PRA and NRA are very helpful in determining accommodative
dysfunction (Weisz, 1983). A low NRA reveals accommodative spasticity;
a very low PRA on the other hand, suggests that the focusing system may
be prone to tiring after concentrated near work.
Accommodative measurements
The different accommodative components listed above require different
methods of measuring accommodative ability and yielding dioptric results.
There is no method in use that describes the complete accommodative
function or even some of the functions put together, nor do we use the same
measuring system for the different dioptric results. Since there is no
method to combine the results of various accommodative components, we
need to find out whether any existing method can be useful in identifying
an accommodative dysfunction of any kind. The following tests are in use:
Amplitude tests:
Donders push-up method: This makes use of a RAF
ruler (Figure 9).
Figure 9. Instrument for
measuring the closest focus
distance in diopters (D), the
RAF ruler.
Sheard´s (1957) method: Here, minus lenses are
added at far distance, monocularly or binocularly,
until blur at distance occurs.
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B. STERNER. OCULAR ACCOMMODATION.
Facility tests:
±2.00 D flip lens test: This is used to measure the
exertion and relaxation change of the
accommodation in cpm (see also page 9,
”accommodative facility”, Figure 7).
Relative accommodation: In this test, changing the
accommodative stimulus assesses the
accommodative flexibility.
Objective tests:
Dynamic retinoscopy: This is used to establish the
degree of lag of accommodation (Leat & Gargon,
1996).
Infrared optometers, e.g., a power refractor: These
are used to examine the eyes for defects of
refraction.
Miscellaneous tests:
Binocular cross cylinder at near distance: With this,
the magnitude of the dioptric reading addition is
established while the subject focuses a near distance
object.
Comparing cycloplegic and manifest refraction:
This is done to objectively look for refractive
differences (e.g., accommodative spasm or latent
hyperopia) using retinoscopy.
Accommodative dysfunction
Presbyopia
The ability to accommodate slowly deteriorates through life and during the
fifth decade of life insufficient accommodative ability becomes a manifest
problem for the emmetrope. The amplitude of accommodation has
decreased to a level of approximately 4 D (Koretz & Handelman, 1988)
and focusing at normal reading distance either requires longer arms or
proper optical aids. This condition is called presbyopia (Duane, 1912) and
the decrease of the accommodative amplitude continues until the amplitude
of accommodation almost reaches 0 D.
The development of presbyopia is not well understood, and there are
theories that attempt to explain its mechanism (Bito, 1988; Fisher, 1988;
Atchison, 1995; Beers & Van der Heijde, 1996). Although presbyopia
means “vision of old age”, its onset can rarely be chronologically defined
because it varies with coexisting ametropia, illumination, target size and
B. STERNER. OCULAR ACCOMMODATION.
15
distance, the effect of drugs, arm length, geographic latitude, and
psychological factors (Michaels, 1987).
Dysfunction
The accommodative system at young age is fairly flexible and resistant to
fatigue (Berens & Sells, 1944). However, in clinical practice,
accommodative dysfunction occurs among pre-presbyopic patients. Often
patients complain of symptoms that appear when doing near distance work.
The refractive status can be emmetropic or slightly ametropic but this is not
always in relation to the patients’ complaints. There is, as mentioned
previously, no simple standard procedure for examination of the
accommodative system including all its facets. Because of the lack of such
method, and the fact that we do not have any simple method to treat
accommodative problems, the accommodative system is not routinely
examined. Still it is of great importance to identify a dysfunction so that
unnecessary near vision problems may be prevented. It is essential to
identify any accommodative deficiencies in young individuals as soon as
possible after school start. Because the focusing system of the eyes has a
contribution in the learning process (Flax, 1970; Sucher & Stewart, 1993),
any accommodative deficiency can make it unnecessarily difficult for the
child to read and develop in school. If the child does not prevent his or her
difficulties to accommodate he or she may always harbor a dislike for near
distance work. Therefore, we need to find a simple and easy-to-use method
that identifies and diagnoses an accommodative dysfunction.
It can be difficult to group accommodative dysfunctions because the
boundaries are often unclear. However, clinically it is useful to separate
anomalies of accommodation into one of five distinct syndrome categories
(Walsh & Hoyt, 1969b; Duke-Elder, 1971):
•
•
•
•
•
Insufficiency of accommodation
Infacility of accommodation
Fatigue of accommodation
Spasm of accommodation
Paresis of accommodation
These five syndromes all constitute different accommodative disorders,
with a different impact on the accommodative function (Table 3).
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B. STERNER. OCULAR ACCOMMODATION.
Asthenopia
Different symptoms associated with accommodative dysfunction are also
listed in Table 3. Asthenopia is a term used to describe eyestrain or
symptoms associated with the use of the eyes (Millodot, 1986). In Figure
10, the most common causes of eyestrain are illustrated.
Table 3. Diagnostic criteria with respect to accommodative dysfunction, and the
incidence of related findings and symptoms.
•
••
Occasional incidence
Frequent incidence
Diagnosis
Insufficiency of
accommodation
Fatigue of
accommodation
Spasm of
accommodation
Paresis of
accommodation
Infacility of
accommodation
Reduced
relative
accommodation
Reduced
accommodative
facility
Associated
symptoms
*
••
Reduced
ciliary
muscle
function
•
•
•
••
•
••
••
••
••
••
••
••
••
••
••
••
••
••
••
••
••
••
••
Reduced
accommodative
amplitude
* Asthenopia, blur, headaches, diplopia, accommodative facility problems,
photophobia, and reading problems are the most frequently reported symptoms
indicating accommodative dysfunction (Hoffman and Rouse, 1980; Daum, 1983a;
Hennessey et al. 1984).
17
B. STERNER. OCULAR ACCOMMODATION.
Accommodative
insufficiency
Accommodative
infacility
Accommodative
fatigue
Accommodative
paresis
Accommodative
spasm
Uncorrected
hypermetropia
Concentration
difficulties
Uncorrected
astigmatism
Uncorrected
presbyopia
Dyslexia
Asthenopia
Neurological
reasons
Hysteria
Aniseikonia
Improper
illumination
Heterophoria
Latent
nystagmus
Retinal/eye
disease
Musculus rectus
medialis
dysfunction
Ocular inflammation,
pain in the eye,
dry eye
Figure10. Illustration of different causes of asthenopia.
Insufficiency of accommodation is a condition in which the amplitude of
accommodation is chronically below the lower limits of the expected
amplitude of accommodation for the patient’s age
(VonNoordenetal.,1973; Daum, 1983b). Morgan (1944b), in describing
various diagnostic criteria, states that insufficiency of accommodation
occurs when the accommodative amplitude is reduced by more than 2 D
below Duane’s expected values for age (1912). Daum (1983b) uses a
criterion on 2 D below Hofstetter’s equation for the minimum amplitude by
age. However, there is no consensus regarding the criteria for making the
diagnosis. In a recent study (Cacho et al. 2002) a summary of nine different
studies of insufficiency was given, all with different criteria. Most of the
criteria contained the equations presented by Hofstetter (1950). Symptoms
include headache, asthenopia, inability to focus on near objects or to
sustain clear vision for a reasonable period of time. A study on nine
children aged 9–16 years (Matsuo & Ohtsuki, 1992) with low
accommodative amplitude in both eyes reports that the subjects had severe
complaints of asthenopia, diplopia, and difficulty in reading. The clinical
recognition of accommodation insufficiency is important in preventing
unnecessary frustration in young school children (Chrousos et al., 1988).
18
B. STERNER. OCULAR ACCOMMODATION.
Infacility of accommodation is the condition in which the ability to rapidly
change accommodation from far to near distance is failing, or in which a
rapid change of accommodation induces symptoms such as asthenopia,
headache, and blur (Hennessey et al., 1984). It differs from accommodative
insufficiency in that clear vision is eventually achieved (Michaels, 1987).
Diagnostic criteria for accommodative infacility are an NRA and PRA of <
±1.75 D (Morgan, 1944b; Hennessey et al., 1984) and/or a facility test
using the ±2.00 D flip test showing 1 SD below the mean of 3 cpm
(Hennessey et al., 1984). If changing fixation from distance to near takes
more than 1 second an abnormal condition is likely to be present (Daum,
1983a).
Fatigue of accommodation is described as the inability of the ciliary muscle
to maintain contraction while viewing a near target with a resulting shift in
accommodation toward the far point (Pigion & Miller, 1985; Owens &
Wolf-Kelly, 1987; Schor & Tsuetaki, 1987).
Spasm of accommodation is a constant or intermittent involuntary and
inappropriate ciliary contraction (Rutstein et al., 1988; Goldstein &
Schneekloth, 1996). It may be unilateral or bilateral. Symptoms include
distance and/or near blur, visual distortion, a drawing or pulling sensation,
and possibly intermittent or persistent diplopia (Michaels, 1987). Also, a
dynamic retinoscopy shows a lag of <±0.00 D (Rouse et al., 1984).
The most common cause for paresis of accommodation is topical
cycloplegia, whether deliberate or inadvertent. Such palsy is generally
unilateral, transient, and evident from a patient’s history (Michaels, 1987;
Mutti et al., 1994). Accommodative paresis can also be functional owing to
weakness or fatigue of the ciliary muscle (Duke-Elder, 1971).
However, a person’s ability to perform a nearpoint task may be impaired
due to the accommodative syndromes listed above if, for example, his or
her accommodative facility is deficient despite having sufficient
accommodative amplitude (Hennessey et al., 1984). It is therefore essential
to identify the exact cause of accommodative dysfunction in order to
alleviate symptoms, improve accommodation efficiency, and decide on the
type and extent of treatment.
B. STERNER. OCULAR ACCOMMODATION.
19
Accommodative therapy
Accommodative dysfunction is not an uncommon visual anomaly and the
symptoms generally occur during the performance of nearpoint tasks
(Daum, 1984). Dysfunctions of accommodation, which have been treated
by optometric intervention, are usually clinically classified as those
dysfunctions mentioned previously, namely accommodative insufficiency,
accommodative spasm, accommodative fatigue, and accommodative
infacility (Suchoff & Petito, 1986), with insufficiency and infacility as the
most frequent forms of dysfunction (Daum, 1983a). After ruling out
neurologic, pharmaceutical, or general health causes, the treatment of a
dysfunction is generally a plus lens addition or orthoptic exercise
(Hoffman, 1982; Bobier & Sivak, 1983; Cooper et al., 1987).
In cases of accommodative insufficiency, treatment consists of either
providing proper distance refractive correction, a plus add for near, or both
(Goss, 1992), or orthoptic exercises aimed at strengthening the
accommodative or vergence mechanisms, such as “push-up” training or flip
lens training (Daum 1983b).
A plus lens addition is recommended in cases of an excessive lag in
accommodation, very low PRA (< –1.5 D), difficulty in performing the
minus lens part of the ±2.00 D facility test, or fatigue during the facility test
(Weisz, 1983). The prescription can be in the form of either normal reading
glasses or a bifocal solution.
Orthoptic excercise is indicated when there is spasticity in the
accommodative system or the accommodative system is poorly controlled
(Cooper et al., 1987). It is also indicated if the patient cannot clear the
initial plus lens flip on the ±2.00 D or if the NRA is low (i.e., <+1.5 D).
Orthoptic excercise is a sequence of activities individually prescribed and
monitored by the examiner to develop efficient visual skills and processing.
One particular method in orthoptic excercise is the flip lens technique. A
“flipper”, as described previously, is a holder with two minus lenses and
two plus lenses (Figure 7). The subject focuses through one pair of lenses
at an object at near distance (40 cm). When the object is clearly focused, a
flip is quickly performed to the other lens pair and the subject focuses
through this. The process is then repeated.
There is scientific and clinical evidence to support the efficacy of using
facility therapy techniques to “strengthen” or improve accommodative
function (Wold et al., 1978; Liu et al., 1979; Weisz, 1979;
20
B. STERNER. OCULAR ACCOMMODATION.
Levineetal.,1985; Hung et al., 1986; Rouse, 1987; Ciuffreda & Ordonez,
1998;Sterner et al., 1999; Ciuffreda, 2002).
B. STERNER. OCULAR ACCOMMODATION.
21
OBJECTIVES
Overall aim
The aims of the present work have been firstly to study how sufficient the
accommodation functions in otherwise healthy children and to identify and
characterize symptoms related to accommodation. Secondly, to evaluate an
accommodative facility training technique in children with impaired
relative accommodation. It is important to ascertain how accommodation
functions in younger ages, how to identify a dysfunction, and to evaluate
treatment, before conclusions can be drawn about other groups such as
visually impaired pre-presbyopes with accommodative dysfunction.
Specific aim: Paper I
The knowledge regarding accommodation in younger ages is rather limited.
An extrapolation of Duane’s data using Hofstetter’s age amplitude formula
suggests high amplitude of accommodation in younger ages. This could
perhaps explain why younger children are in some extent neglected due to
the expectation of sufficient accommodative ability. Such extrapolation
may therefore give a false impression because accommodative
dysfunctions among school children at any age might create near working
related problems. The aim of this study was to describe accommodation in
junior level school children and to compare these data with both Duane’s
data and Hofstetter’s equations.
Specific aim: Paper II
The occurrence of subjective symptoms related to accommodative
dysfunction at near among otherwise healthy young school children is not
fully investigated. The aim of this paper was to study the relation between
subjective symptoms at near to the accommodative function in terms of the
amplitude and of the relative accommodation. A secondary aim was to
explore adequate reference values.
Specific aim: Paper III
The specific aim of this study was to examine the effect of flip lens training
on the accommodative function in a group of children with accommodative
dysfunction and symptoms such as asthenopia, headache, blurred vision,
and avoidance of near activity. Another aim was to study whether flip lens
training increases accommodative facility, and to establish whether it may
have long term positive effects on the subjects’ asthenopia and related
problems.
22
B. STERNER. OCULAR ACCOMMODATION.
Specific aim: Paper IV
The aim of Paper IV was to further study the effect of accommodative
facility training on relative accommodation. As part of the study, a
comparison was made between traditional dioptric flipper treatment and a
sham flipper treatment to establish whether it was the treatment as such that
affected the subjects’ accommodative performance or whether the
additional care giving of the children had an influence.
23
B. STERNER. OCULAR ACCOMMODATION.
SUBJECTS
Paper I & II
A junior level school in the Göteborg area was chosen at random and all
the children at this school were invited to freely and voluntary participate
in the study. There were 136 children in the age range 6-10 years. The
examination took place at school, and informed consent was obtained from
the parents. Among all the 136 children, 28 declined participation, and 31
did not answer the invitation. Seventy-seven children were enrolled and all,
except for one boy who did not turn up, were examined. After examination,
four children were excluded due to a high astigmatism. Thus the study
included 72 children, 43 boys (mean age 8.1 years) and 29 girls (mean age
8.3 years).
Paper III
Altogether 38 children aged 9–13 years were selected for this study. The
children were referred by School Health Care for near work-related
problems and for complaints of headaches, blurred vision, asthenopia, loss
of concentration, and avoidance of near activity. We included only children
with reduced NRA and PRA and/or a very slow accommodative facility.
(Table 4 shows the values of the NRA and the PRA among the children in
this study compared to the diagnostic criteria for accommodative infacility
from Morgan, 1944b).
Table 4. Mean relative accommodation (± SD) before training and for controls
compared to the values presented by Morgan (1944b) as the diagnostic criteria for
accommodative infacility.
Mean NRA
Mean PRA
Before training
Controls
Morgan, 1944b
+ 1.25 ± 0.4 D
- 1.3 ± 1.0 D
+ 2.0 ± 0.2 D
- 3.9 ± 1.3 D
< + 1.75 D
< - 1.75 D
Before entering the children into the training program, their
accommodation, cycloplegic refraction, and visual acuity at distance
(decimal notation) were examined. In all children, binocular vision,
stereopsis, and motility were tested by an orthoptist. All the parameters
were in normal range. All of the 38 children in the study were interviewed
by telephone before the long-term follow-up examination 2 years after the
conclusion of accommodative facility training.
24
B. STERNER. OCULAR ACCOMMODATION.
Normative data were established using 24 voluntary controls aged 9–13
years.
Paper IV
Thirteen Swedish children, five girls and eight boys aged 9–11 years, were
included in the study. They were referred by the same inclusion criteria as
used for the children in Paper III.
B. STERNER. OCULAR ACCOMMODATION.
25
METHODS
Paper I
Accommodative amplitude measurements was performed with Donder’s
push-up method using a R.A.F. Near Point Rule (Figure 9), a rod with a
movable target and metrics as well as dioptric markings, placed on the
childs forehead. The child had distance correction in place and the movable
target was slowly moved towards the child along the ruler until the child
reported blurring and the dioptric result were then recorded.
Determinations were made both monocular as well as binocular, and all
measurements were repeated three times and the average distance was
recorded in diopters.
For comparisons, Hofstetter’s equations for minimum, expected, and
maximum amplitude by age was calculated (minimum = 15 - 0.25 · age,
expected=18.50.3·age, and maximum = 25 - 0.4 · age (Figure 11)).
Figure 11. The same diagram as Figure 6, from Duane (1912), now including plots from
the three prediction formulas (minimum amplitude = 15 - 0.25· age, expected amplitude
= 18.5 - 0.3 ·age, and maximum amplitude = 25 - 0.4 ·age) by Hofstetter (1950).
26
B. STERNER. OCULAR ACCOMMODATION.
Paper II
A questionnaire containing four different questions linked to four different
subjective symptoms (headache, asthenopia, floating text, facility
problems) was used. The amplitude of accommodation and the relative
accommodation were recorded. The relative accommodation, both positive
and negative, was measured using the method described in Hung &
Ciuffreda (1994).
Paper III and IV
To establish relative accommodation, both positive and negative, we used
the method described in Hung & Ciuffreda (1994), same as in paper II.
For accommodative facility training, the children were requested to use a
dioptric flipper (Figure 7). A high compliance was demanded. Therefore,
the children as well as their parents were given wide instructions before the
onset of the treatment and the compliance was monitored after every
examination. As far as could be determined the children were in
compliance with the prescribed treatment. After careful instructions the
training was done by each child at home following a protocol. An
optometric examination was performed every second week to ensure high
compliance. In Paper IV the children in the sham group started with
2weeks of training with plano lenses instead of dioptric lenses. After these
2weeks with plano lenses they changed to dioptric lenses and continued
the training. If a subject showed a hypermetropia, plus lenses were
prescribed after the first or second optometric examination for proper
progression of the accommodative facility training. The necessity of
correcting this grade of hypermetropia might be questionable due to the
training effect. However, since they are symptomatic it is irresponsible not
to correct them apart from the training effect. To correct this amount of
ametropia is also what is recommended in the literature when to correct a
hypermetropia in symptomatic individuals (O´Leary and Evans, 2003). The
training continued until the subjects reported that the symptoms were gone.
The Committee for Ethics at The Sahlgrenska Academy, Göteborg
University, Sweden, approved the studies.
B. STERNER. OCULAR ACCOMMODATION.
27
RESULTS
Paper I
The result showed lower accommodative amplitude than expected in a
large group of children and not equivalent to the expected age values.
Especially monocular measures which revealed an average difference from
Hofstetter’s expected of –3.60 D (-4.5, -2.8) (right eye) (p<0.001) and
–3.50 D (-4.4, -2.7) (left eye) (p<0.001). The binocular measures were
higher; nevertheless, the average difference from the expected line was
–0.80 D (-1.7, +0.1) (p = 0.072). Therefore, we found statistically
significant differences between our monocular data and that from
Hofstetter’s equations. The average difference of the binocular
observations was not statistically significant.
Paper II
More than one third of the children (34,7%) reported at least one symptom
when doing near work and the most frequent reported symptom was
asthenopia (26,4%). The subjective symptoms emerged at the age of 7.5
years and the relation between different accommodative parameters to
subjective symptoms was significant. The discrimination ability between
the amplitude of accommodation, both monocular and binocular, was
significant (right eye p = 0.013, left eye p = 0.019, and binocular p =
0.004), and the monocular amplitude was in average approximately two
diopters lower in the symptom group compared to the group without
symptoms. Regarding binocular amplitude the average difference was
approximately three diopters. Also NRA showed significant discrimination
ability (p=0.008) but there were no statistical significances regarding PRA
(p>0,20). A table with different diagnostic reference values for
accommodative insufficiency in terms of sensitivity, false positive rate and
positive predicting value is presented as an assistance for the possibility to
link the reference values to a risk for consequences for the patient.
Paper III
Symptoms such as headache and asthenopia, gradually decreased in all 38
children and finally disappeared during the training period. The length of
the training period varied from 3 weeks to 25 weeks, with the training
period being less than 8 weeks for the majority of children.
Mean NRA as well as mean PRA increased during treatment. However, the
post-training results for both NRA and PRA were significantly lower than
the data on the controls. In other words, there was a statistically significant
increase in both NRA (p<0.0001) and PRA (p < 0.0001) during the
28
B. STERNER. OCULAR ACCOMMODATION.
training period although both the parameters PRA and NRA were
significantly lower than the results obtained among the controls (viz. p =
0.024 for NRA and p < 0.0001 for PRA).
The results from the facility tests is exemplified in Figure 12 (a, b). The
time was measured when changing from the PRA value to the distance
correction (a) and from the distance correction to the NRA (b) both before
and after the training period. The result from the distance correction to the
PRA and from the NRA to the distance correction is not illustrated in
figures, but the trend was approximately the same.
A follow-up examination was performed 2 years after the final
examination. None of the children had any dioptric training during the time
that elapsed from the conclusion of training to the follow-up examination.
Both NRA and PRA were almost the same at the conclusion of training as
at the follow-up examination and none of the children had regained any
symptoms.
Paper IV
In the sham group, flipper treatment was divided into three periods, with an
initial 2 weeks of (accommodative facility) training using a plano lens
flipper as the sham treatment. This sham period had no effect on the
symptoms (i.e., headaches, asthenopia, blurred vision) of the patients. In
the following 2 weeks a ±2.00 D flip lens set was used and by the end of
this period some symptoms had vanished. The period of accommodative
facility training was extended until all of the patients were free from
symptoms. This extended period starting in the fifth week of training varied
with each case.
There was a decrease in both mean NRA and mean PRA during the first
period of training while the patients used plano lenses. This decrease was
recovered in some of the patients during the next 2 weeks when a ±2.00 D
flipper was used. The traditional treatment group who started their training
with a ±2.00 D flip lens showed an increase in their mean relative
accommodation at each examination. Their symptoms vanished by the end
of the training period.
The results show that the first weeks of dioptric training in the sham group
as well as the traditional group showed an effect of the dioptric training,
and the training had an effect for the whole of the training period in all
subjects. In concordance with this is the fact that the plano lens flipper did
not have any positive effect on either mean NRA or mean PRA in any
29
B. STERNER. OCULAR ACCOMMODATION.
Facility in seconds from PRA value to distance correction
35
Number of children
30
25
20
Before training
After training
15
10
5
0
1
5
10
15
20
25
30
35
40
45
50
Time in seconds
Facility in seconds from distance correction to NRA value
35
Number of children
30
25
20
Before training
After training
15
10
5
0
1
5
10
15
20
25
30
35
Time in seconds
Figure 12. To present the result from the accommodative facility measurements, in
terms of quickly changing the accommodation from exertion to relaxation, the time was
measured when changing from the PRA value to the distance correction (above) and
from the distance correction to the NRA (below), both before (filled staples) and after
(open staples) the training period.
30
B. STERNER. OCULAR ACCOMMODATION.
patient in the sham group. It is, however, difficult to explain why the PRA
value actually decreased during the sham period for all the patients in the
sham group. If there are any placebo effects we should in fact expect an
increase instead of a decrease in the relative accommodation values during
the sham period. Our data show a significant increase in both mean NRA
and mean PRA in both the sham group and the non-sham study group
during the dioptric training despite some individual variations in the results.
B. STERNER. OCULAR ACCOMMODATION.
31
DISCUSSION
The knowledge of how the neuronal accommodative complex functions are
in some aspects still limited. In young persons the accommodation is
expected to be flexible and powerful without any closer control of its
sufficiency. In 1912, Duane stated according to his measurements, that the
amplitude of accommodation is high at young ages. Furthermore, Berens &
Sells (1944) stated that in young ages the accommodative system is quite
flexible and resistant to fatigue. Even though this is old data it is still what
we normally believe about ocular accommodation. If a person shows
subjective symptoms when reading, a control of the accommodative
function is therefore not always the primary function that is taken under
consideration in an examination. However, accommodative dysfunction
does occur among pre-presbyopic patients in clinical practice. These
patients often complain of symptoms that appear when doing near distance
work. The refractive status can be emmetropic or slightly ametropic, but
this is not always in relation to the patients’ complaints. There is no simple
standard procedure including all the accommodative facets for examination
of the accommodative system. The accommodative system is not routinely
examined because of the lack of such method, and in addition to the
presumption mentioned above. We used Donders’ push-up method to
establish the amplitude of accommodation. Even though it solely measures
the amplitude of accommodation it is commonly the method used to
diagnose any abnormality of accommodation.
The results from Paper I showed lower amplitude of accommodation than
expected among a considerable number of children. Whether these children
also suffered from subjective symptoms at near that might be related to
insufficient accommodation was examined in Paper II. The results imply
that there is a need for clinical routines for examining the accommodative
function as part of the ophthalmic or optometric examination. To expect
that young children should possess high amplitudes of accommodation
perhaps inhibits practitioners from making careful measurements of the
accommodative amplitude, which Donders (1864) pointed out as
fundamental in making a diagnosis.
Unnecessary near vision problems may be prevented if a dysfunction is
identified. For example, it is essential to identify and possibly treat any
accommodative deficiencies in young individuals as soon as possible after
school start. Since the focusing system of the eyes contributes to the
learning process (Flax, 1970; Sucher and Stewart, 1993) any
accommodative deficiency can make it unnecessarily difficult for the child
32
B. STERNER. OCULAR ACCOMMODATION.
to read and develop in school. If the child does not alleviate or reduce his
or her difficulties of accommodation he or she may always harbor a dislike
for near distance work.
In Paper II a questionnaire for identifying subjective symptoms related to
accommodation was used. The questionnaire contained four different
questions related to four different symptoms that, according to previous
studies (Hoffman and Rouse, 1980; Daum, 1983a; Hennessey et al. 1984),
are the most frequent related subjective symptoms to an accommodative
dysfunction. Using these questions we were able to identify subjective
symptoms in a considerable group of children studied. Asthenopia and
headache were the most frequent symptoms in these children.
The questionnaire did not give any information about grade or intensity of
each symptom. A qualitative evaluation of the symptoms might therefore
further refine the linkage to an accommodative dysfunction. A follow up
would be necessary to be able to study whether symptoms remains or
disappear without treatment over time for these children,. That would also
give information of what happens with the accommodative ability over
time.
There were no subjective symptoms before the age of 7.5 years. This is
probably due to the increasing demand on their near sight at school at these
ages and symptoms will probably not appear until then. Children below the
age of 7.5 years with low accommodative amplitude who are not yet
frequent readers may develop subjective symptoms later due to their low
amplitude.
There was a significant relationship between different accommodative
parameters and subjective symptoms, especially “asthenopia” and
“headache”. The amplitude of accommodation was of no use in diagnosing
the less frequent symptoms “floating text” and “facility problems”. This
does not necessarily imply that there is no relationship between amplitude
and these symptoms. It is likely that the relation between symptoms and
questions is not obvious to the children or that the non-significance is due
to the limited sample size and the low frequency of these symptoms.
We need to have clear standards for defining accommodative insufficiency
(AI) and suitable choices of reference values to identify children with risk
of developing an AI. If we have a low reference value we will probably
miss many cases with AI that will benefit from treatment but there will be
less cases of false positive. On the other hand, if we increase the reference
B. STERNER. OCULAR ACCOMMODATION.
33
value we will have a better sensitivity even though we will obtain some
cases with sufficient accommodation without causing symptoms.
A longitudinal follow up of the children in this study would of course
facilitate the decision of suitable reference values. A table is presented
(Table 7 in Paper II) which shows the different levels of sensitivity and
positive/negative prediction values from four different reference values for
children aged 7.5 to 10 years in this cross-sectional study. It can be
discussed which value to choose but the value close to the lower quartile
could be suitable. Then there will be a sufficient positive predicting value
and a reasonable number of cases of false positive. Possibly the prediction
could be improved by performing a follow-up to capture more persisting
and clinically more relevant symptoms.
The patients included in Paper III and IV were selected from among
children with problems at school related to near work. It was found that all
of the selected patients had reduced relative accommodation and the
majority of them had a slow accommodative facility. None of the patients
could be classified as having the syndrome called convergence and
accommodative insufficiency as described by Von Noorden et al. (1973).
The studies in Paper III and IV were performed to investigate the
possibility of increasing or improving accommodative function as being the
probable main problem of these patients. We therefore tried to accomplish
three goals: firstly, to quantitatively examine the effect of accommodative
facility training on relative accommodation; secondly, to determine
whether symptoms (headache, blur, asthenopia) disappeared with increased
accommodative facility; and thirdly, to establish whether the dioptric
training had any long-term effects.
Accommodative insufficiency and accommodative facility training have
been discussed in the optometric literature mainly during the past few
decades (Hennessey et al., 1984; Daum, 1983b; Cooper et al., 1983;
Cooper et al., 1987; Rouse, 1987; Chrousos et al., 1988; Russel & Wick,
1993; Ciuffreda, 2002), predominantly with regard to pre-presbyopic
patients (Zellers et al., 1984; Cooper et al., 1987; Russel & Wick, 1993).
The close relationship between accommodative deficiency and related
visual symptoms, such as blurred vision, asthenopia, loss of concentration,
and avoidance of near activity, has been pointed out. Among the findings
listed by Hoffman & Rouse (1980), as indicative of accommodative
difficulties when associated with symptoms, we focused on two items: a
NRA and PRA of <±1.75 D, and a ±2.00 D flipper test result, measured
monocularly and binocularly, of <12 cpm.
34
B. STERNER. OCULAR ACCOMMODATION.
The proposed relationship between restricted relative accommodation and
symptoms was in concordance with our findings. The results of these
studies support to some degree the idea that a PRA and a NRA of <±1.75 D
(Morgan, 1944b; Hennessey et al., 1984) are related to the presence of
symptoms (i.e., headache, blurred vision, asthenopia, loss of concentration,
and avoidance of near work).
Our studies show that accommodative facility training can increase both
positive and negative relative accommodation in selected patients, as well
as relieve them of their symptoms. The studies also clearly indicate that
there is a long-term effect of accommodative facility training using a
dioptric flip lens technique. However, it is not clear from our studies
whether the relief of symptoms was linked to an increase in relative
accommodation or to an improvement of the accommodative facility, or
both. We also do not know whether further accommodative training would
have further increased the accommodative function.
The fact that all the children became free from subjective symptoms after
training might be discussed in relation to the knowledge from medical
treatment in terms of rate of success; that it is not successful in all patients.
However, the phenomenon of training is improvement, which also was the
object in this study. As a group, the children’s accommodative function
was not normalized, but improved enough to release all the children from
their subjective symptoms
Since the question has been posed whether it is the actual use of dioptric
training that causes an increase in relative accommodation or whether
unspecific training and caring can lead to such increase we studied the
effect of sham treatment in seven patients given such treatment before the
dioptric training. The findings clearly indicated that short-term sham
treatment, if anything, had a negative effect on relative accommodation and
no observable effect on symptoms.
The lack of a positive effect of the sham treatment with plano lenses
strongly suggests that the therapeutic effect of dioptric treatment of the
accommodative facility is linked to the effect of the ±2.00 D flip lenses.
The focus of this study was to examine changes in relative accommodation
in relation to treatment. The fact that the effect on the relative
accommodation of 2 weeks of dioptric training following the sham
treatment was as marked in this group of patients as it was in the traditional
training group starting directly with dioptric training further links the
positive effect on relative accommodation to the use of the ±2.00 D flip
lenses.
B. STERNER. OCULAR ACCOMMODATION.
35
The fundus examination in an ophthalmologic examination of the eye,
gives the examiner much information needed for proper diagnosis.
Sometimes the examiner observes that the optic disc shows abnormalities,
which indicates further examinations. The abnormality can be due to an
abnormal fundus morphology, which in some cases may influence the
visual function. Preliminary observations (Hellström et al. in preparation)
suggest that children with impaired relative accommodation in many cases
also have optic disc abnormalities and/or peripapillary pigmentation
(Figure 13).
a.
b.
Figure 13. Fundus photographs of (a) a 13-year-old girl with impaired relative
accommodation demonstrating an optic disc with peripapillary pigmentation, and (b) a
13-year-old girl from a control group without any peripapillary pigmentation.
The etiology of these optic disc abnormalities is not yet fully understood.
However, these findings suggest involvement of congenital factors at least
in some cases of impaired relative accommodation.
Information about the natural history of accommodative dysfunction in
children is lacking, and we do not know whether an insufficient
accommodation spontaneously improves with age. However, our clinical
experience is that an accommodative infacility lasts for years even though
the effect of maturation cannot be excluded from the present study design.
The facility training had a positive effect on both mean PRA and mean
NRA as well as the symptoms, and offers the possibility of at least
shortening the period of symptoms and withdrawal from near work at
school at a stage in schooling that is academically important.
The results, in terms of the dioptric treatment, in this study is in agreement
with results reported previously in the literature (Daum, 1983b; Cooper et
al., 1987; Siderov, 1990; Russel & Wick, 1993; Ciuffreda, 2002), although
accommodative insufficiency has been more commonly reported in pre-
36
B. STERNER. OCULAR ACCOMMODATION.
presbyopic individuals than in school children (Hennessey et al., 1984;
Cooper et al., 1987; Russel & Wick, 1993; Scheiman et al., 1996).
The result further raises the question whether the facility training method is
a useful method for other aspects of the ophthalmologic practice, such as in
diagnosing and training an accommodative dysfunction among visually
impaired children (Woodhouse et al., 1993; Leat, 1996). An
accommodative impairment can in some cases be hidden in an incorrect
interpretation of eye disease and associated symptoms. The contact person
of the child may conclude that the child’s difficulties in performing near
work are the result of eye disease instead of being due to an
accommodative impairment.
B. STERNER. OCULAR ACCOMMODATION.
37
CONCLUSIONS
The ocular accommodation in young children is not as sufficient as we
expect. Young school children may have an insufficient accommodative
ability that causes subjective symptoms when reading. These symptoms
have shown to emerge in these children from the age of 7.5 years. Further
studies which follow children over time to see if low accommodative
amplitude generates subjective symptoms and to prove causality are highly
desirable.
This study has also characterized a group of children with impaired relative
accommodation. They were relieved of subjective symptoms as a result of
dioptric training and they improved both their NRA and PRA. The training
intensity and spacing of training sessions over a considerable period still
need further evaluation in order to optimize the training and the diopter
value of the lenses.
It is essential to identify accommodative dysfunction in order to alleviate
symptoms, improve accommodation efficiency, and decide on the type and
extent of treatment. It is also of utmost importance for a direct and
successful treatment that children with accommodative dysfunction be
properly diagnosed and that other ophthalmologic problems be excluded.
38
B. STERNER. OCULAR ACCOMMODATION.
FUTURE STUDIES
• A longitudinal follow up study is designed which will give us
information on the stability of accommodation over time in the
children included in paper I and II. Such a follow-up will also give
information on whether the symptoms remain or disappear without
treatment over time and facilitate the decision of suitable reference
values.
• A study on accommodation in visually impaired children and how
the results from the present studies can be translated to these children
has started.
B. STERNER. OCULAR ACCOMMODATION.
39
TACKORD (Acknowledgments in Swedish)
Bland alla de personer jag vill tacka för all den hjälp och allt det stöd jag
fått i arbetet med denna avhandling, vill jag börja med att sända ett stort
tack till Maths Abrahamsson, min förste handledare som tyvärr gick bort
alldeles för tidigt. Med optimism och uppmuntran kryddat med allehanda
skämt och anekdoter var han den förste att introducera och intressera mig
för forskning. Tack Maths, för allt du gav.
Anders Sjöström, som utan att tveka tog mig under sina vingar som ny
handledare. Fastän Maths och jag hade bollat olika idéer om projekten som
ej hann bli nedtecknade satte sig Anders snabbt in i arbetet och ytterligare
hjälpte mig att utveckla och förbättra projekten. Tack Anders, för all din tid
och för allt ditt jobb och för att du med sådan smittande entusiasm bistått
mig till att slutföra avhandlingsarbetet. Tack också för att du lärt mig hur
man tillagar en äkta “WildWest Dinner”.
Johan Sjöstrand, min bihandledare, för din kunskap och klokhet som jag
och vi andra på avdelningen alltid kan få luta oss mot och få hjälp av och
för att du alltid är så positiv och glad.
Martin Gellerstedt, min medförfattare, för ett gott samarbete och excellent
statistisk rådgivning.
Ulf Stenevi, Ann Hellström och Bertil Lindblom, för intressanta och
givande kommentarer, och ett särskilt tack till Ann för värderingen av
ögonbottenbilderna.
Jörgen Thaung och Zoran Popovic, för att ni alltid är så snälla och
hjälpsamma med allehanda ting och i synnerhet när det kört ihop sig med
datorn. Ni är brillianta!
Melanie Baumann, för din ortoptiska expertis.
Stefan Michélsen, för givande diskussioner och råd kring optik och
optometri.
Eva Berglund och Anki Nyberg, för er hjälp med många administrativa
saker.
40
B. STERNER. OCULAR ACCOMMODATION.
Alla kollegor och vänner på och runt sektionen för oftalmologi och särskilt
Gunilla Magnusson, Josefin Ohlsson, Karin Sundelin, Madeleine
Zetterberg, Lada Kalaboukhova, Alf Nyström, Gunilla Brunnström,
Ulla Kroksmark och Maria Kræmer, för er vänskap och generositet i att
dela erfarenheter av att vara forskarstudent och för många trevliga
fikapauser.
Alla mina kollegor och vänner på Syncentralen i Göteborg och ett särskilt
tack till min före detta chef, Lisbeth Axelsson-Lindh.
Min mamma Lena, min brorsdotter Martina, min brorson Anton, och alla
mina vänner, för alla glada tillrop.
Ulrica, min hustru, för all din kärlek och allt ditt stöd. Du är bäst!
Slutligen vill jag tacka alla de barn som deltagit i studierna.
Jag tackar också för ekonomiskt stöd från (i alfabetisk ordning):
Föreningen De Blindas Vänner;
Medicinska forskningsrådet (Anslag nr 02226);
Optikerförbundet;
Sigvard & Marianne Bernadottes Forskningsstiftelse för Barnögonvård;
Stiftelsen Handlanden H Svenssons fond för blinda och synsvaga;
Stiftelsen Karl Simsons Fond;
Stiftelsen Kronprinsessan Margaretas Arbetsnämnd för synskadade;
Stiftelsen Solstickan;
Stiftelsen Sunnerdahls Handikappfond; och
Synoptik-Fonden.
B. STERNER. OCULAR ACCOMMODATION.
41
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